﻿// https://leetcode-cn.com/problems/symmetric-tree/
// 101. 对称二叉树

#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <queue>
#include <limits.h>

using namespace std;

// struct ListNode {
//     int val;
//     ListNode *next;
//     ListNode() : val(0), next(nullptr) {}
//     ListNode(int x) : val(x), next(nullptr) {}
//     ListNode(int x, ListNode *next) : val(x), next(next) {}
// };

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};

class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if (root == nullptr)
            return true;
        return Compare(root->left, root->right);
    }

    bool Compare(TreeNode* left, TreeNode* right) {
        if (left != nullptr && right == nullptr)
            return false;
        else if (left == nullptr && right != nullptr)
            return false;
        else if (left == nullptr && right == nullptr)
            return true;
        else if (left->val != right->val) 
            return false;
        
        bool outside = Compare(left->left, right->right);
        bool inside = Compare(left->right, right->left);
        bool is_same = outside && inside;

        return is_same;
    }
};

int main() {
    Solution obj = Solution();
}